Interesting looking device, but being a typical American my understanding of the German language is rough. How does this device connect to measure up to 400A? There are many capable wattmeters around, but most top out around 100A.

Quote:

Originally Posted by jjmouris

...Many people have the SM Unilog with a 400A sensor in use and it has a nice 16hz recording feature with some spare slots;http://www.sm-modellbau.de/...

Interesting looking device, but being a typical American my understanding of the German language is rough. How does this device connect to measure up to 400A? There are many capable wattmeters around, but most top out around 100A.

Lucky to find this great thread thanks to a post from Wim on the dutch forums. Very good of him and of you for creating this device and the amazing support. Was a great read so far!

A little bit of background on myself and what i spend my time with. Ever heard of the FAI class F5B ? It's some crazy people who insist on pulling way to many amps out of those poor little lipo's for short periods at a time and making our planes go from 100 to 300kph in less then 3 second while going strait up. It's addicting, what can i say. We regularly pull around 100C for about 2 seconds out of around 500 grams worth of Lipo. We generally only discharge the pack down to ~50% charge state. To throw in some more typical numbers, 5KW is about where most competitors are at now, on 5S 3300mah that would be around 300A at 16.5V under load or 3.3V/cell.

I think you can already see how important it is for us to have good cells, make sure out packs are in good health and possibly controll the temperature of the pack. I say that last thing a bit hesitantly as i have been avoiding flying in cold weather (sub 5 deg C) and generally don't bother preheating the packs when i do fly. This means i get less power on the first climb but then the power seems to be very constant for the other remaining 10-12 climbs. In the past this effect was much worse and it would take nearly 5 climbs for the power to level out.

In terms of wear on the packs. I have had no trouble abusing packs like this for more then one flying season and usualy when a new generation comes out the next year, the old ones get moved to the dust collection area anyway. But i do fear that we might get a bit less power nearer the end of the year and an injection of a fresh pack into the mix can have some ''unexpected'' results where suddenly more power is to hand. This is where people run out of their energy allowance as we fly with a total energy limiting device (1750W.min).

Many people have the SM Unilog with a 400A sensor in use and it has a nice 16hz recording feature with some spare slots;http://www.sm-modellbau.de/

I was wondering about maybe seeing if we could somehow connect your unit to a Unilog and run a pack through on a ''tester unit'' to simulate a flight and see how the pack temperature really effects the IR of the pack.

Would love to hear your thoughts on the above and in general. Also i am probably wanting to buy a unit from you.

Kind regards, Joe

Joe,

Thanks for that. I think it would be simply done by connecting the meter in parallel with the load during a simulation. Am on hols in Bavaria at present until July 4th . Will contact you on return

Wayne

PS Just been sitting out on hotel balcony and can see two hotliners being flown in the far distance; just provoking me!

I can see how this meter might be useful to sort the good from the bad packs at the hobby shop before purchasing! I.e., confirm (or more likely, refute!) the C-ratings on the packs.

Which leads to a question...

Can you power the meter with one pack, and measure the cell resistances of another? The relevance of this question becomes obvious when you consider that new packs often have no connector on the main discharge leads, but the balance taps are accessible. Can I use an old pack to power the meter, and measure the IR of the cells of another pack without issue?

Can I use an old pack to power the meter, and measure the IR of the cells of another pack without issue?

All kelvin type ESR meters will require main leads to be attached to the meter in order to get an accurate measurement of individual cell internal resistance. You could fabricate a special lead that engages the balance connector and use the meter in 'pack' mode. This will give you total pack internal resistance plus resistance of wires and connectors but will not allow for accurate internal resistance measurement of individual cells.

When measuring new packs without connectors, I simply stick some sharp probes into the ends of the wires to simulate a pack connector. This allows true kelvin internal resistance measurement of individual cells without having to add a connector to the pack.

An update of my pack IR's. Measured 8 packs just now, temp soaked 23C = 73.4F.
2 packs about a year old (TP 45C), 4 packs a few months old (TP 65C), 2 packs brand new just added 4mm bullets. All the TP packs were flown today, all are only charged at the field and always flown before going home, sometimes a short last flight:

TP 45C 4s 2650mAh
my post from Nov 2010 in this thread:

Quote:

Originally Posted by like2fly!

which have about 90 cycles on each, both bought early this summer on the same day and used in a 3dhs Aspera and 3dhs 51" A J Slick.
At ~21 deg c (~70 f) rounding to 1dp one pack cells are 5.8, 5.8, 5.8, 5.8
The other is 6.2, 6.2, 6.2, 6.2
Alex

These six packs are brand new, never charged, just unwrapped and connectors added. I got the Thunder Powers last week. I fitted 4mm gold bullets to the two 4s packs and 6.5mm CC bullets to the four 5s packs.

All were measured at home yesterday, ambient temperature 20 C (68 Fahrenheit) after having been at 20 degrees centigrade for 6 hours

The proposed uses are:
4s pattern at ~40-45amps WOT on the ground, 3D aero at ~55-60amps WOT on the ground, EDF at ~50-60amps WOT on the ground (which wont decrease on the air).
5s pattern at ~80-90amps WOT on the ground

looks like the connector solder on one of the Gens Ace packs is not so good... I had that feeling when I did it.

Looks like the Gens Ace have a better potential performance with regards IR than the 65C G6 TPs. The 3300 and 5000 TP's are roughly equal. The 25C Gens Ace are 15% better, potentially, Than the 65C TPs, looking purely at my IR readings.

Hi Charles,
I do remember that post of yours, the numbers stood out, the fact that the IR was the same as the 00 prototype TP's at the time. And I recall that the 00's are slightly better than the G6 65C from your numbers.

Im looking forward to getting these Gen Aces in the air to see how they perform. I was supposed to maiden them today (best weather for a while) but the esc didnt arrive and I didnt hulk foam out of the foam habu this am to run them in (the wire on the Gens Ace packs is a rigid 90 deg angle so i need more space in the foam fuse). Handy to have a european stockist too.

Hi all. Very interesting thread, thanks Wayne for your work and everyone else for contributing. Do you have any left or do you think you'll make any more? very interested in one.

A couple of questions. First is probably easy for most but what does ESR stand for?
Next is testing my understanding of the thread and principles. Would it be possible to measure individual cell voltage at the balance tap then put a watt meter in line on the plane run up the motor for a short time to a set current and quickly measure the cell voltage under load before the pack has had much time to warm up. If you then took the voltage difference and divided by the current you ran the motor at would it give you a reasonable IR reading to spot a weak cell?